This is kind of a confusing question for DO students, simply because a lot of DOs shoot for MD residencies which can usually be tougher to get altogether. However, I'll just give a break down of the most competitive in general (from what I've heard)
-Integrated Plastics
-Derm
-Gas
-Radiology
-G Surg
That could be way off but I do know that those are some top ones, and also Neurology should be way up there, but I'm truthfully not sure what you have to complete before it (you might have to surg to neurosurg or something).
... Sorry if this is off, I'm just a pre med (and for some reason I'm really tired and probably shouldn't be on SDN right now!!)